Keep default minor log ticks if there's 1 major & 1 minor tick.

... rather than switching to AutoLocator.

The old logic only checked whether there's two minor ticks, but one
major plus one minor tick works too.

Author: anntzer

lib/matplotlib/tests/test_ticker.py

@@ -356,6 +356,10 @@ def test_switch_to_autolocator(self):
         loc = mticker.LogLocator(subs=np.arange(2, 10))
         assert 1.0 not in loc.tick_values(0.9, 20.)
         assert 10.0 not in loc.tick_values(0.9, 20.)
+        # don't switch if there's already one major and one minor tick (10 & 20)
+        loc = mticker.LogLocator(subs="auto")
+        tv = loc.tick_values(10, 20)
+        assert_array_equal(tv[(10 <= tv) & (tv <= 20)], [20])
 
     def test_set_params(self):
         """

lib/matplotlib/ticker.py

@@ -2522,10 +2522,12 @@ def tick_values(self, vmin, vmax):
 
         if (len(subs) > 1
                 and stride == 1
-                and ((vmin <= ticklocs) & (ticklocs <= vmax)).sum() <= 1):
+                and (len(decades) - 2  # major
+                     + ((vmin <= ticklocs) & (ticklocs <= vmax)).sum())  # minor
+                     <= 1):
             # If we're a minor locator *that expects at least two ticks per
             # decade* and the major locator stride is 1 and there's no more
-            # than one minor tick, switch to AutoLocator.
+            # than one major or minor tick, switch to AutoLocator.
             return AutoLocator().tick_values(vmin, vmax)
         else:
             return self.raise_if_exceeds(ticklocs)